The present invention relates to a rear axle swing restriction system and a rear axle swing restriction method. More specifically, the invention relates to a system and a method for swing restriction of a rear axle of an industrial vehicle, such as a fork lift truck, including a front axle of a rigid axle type and a rear axle of a swing axle type, in which the rear axle is operatively connected relative to a vehicle body at a central part thereof in a transverse direction of the vehicle, so that it is vertically swingable about the connected part relative to the vehicle body, and which has a stopper mechanism arranged between the rear axle and the vehicle body, for restricting an allowable range of the vertical swing.
There is disclosed in Japanese Patent Application Laid-Open Publication No. 6-106930 a fork lift truck as a vehicle including a front axle of a rigid axle type and a rear axle of a swing axle type. FIG. 1 is a front view of the rear axle, partly in section. Left and right rear wheels 1 are rotatably supported on left and right knuckle spindles 3, respectively, and the knuckle spindles 3 are operatively connected by left and right king pins 7 to both ends of steering axle 5 as the rear axle in concern.
The steering axle 5 has at a transversely central part thereof a swing shaft 9 provided therethrough in a longitudinal direction of the vehicle. The swing shaft 9 is operatively supported at its longitudinal ends with a pair of brackets 13 hung from underside of a vehicle body 11, so that left and right portions of the steering axle 5 are vertically swingable relative to the vehicle body 11, about a center of the swing shaft 9 as a swing center S, with effects such as a prevention of a floating of driving front wheels in travel on an undulating road or the like, permitting an improved ride feeling to be comfortable while traveling.
The vehicle body 11 has under left and right sides thereof a pair of stopper bolts 15 downardly projecting therefrom. On the other hand, the steering axle 5 has at corresponding locations thereon a pair of pads 17 for receiving lower ends of the stopper bolts 15, as they are either brought into abutment thereon, to thereby restrict an allowable range of the swing of the steering axle 5 relative to the vehicle body 11.
While the steering axle 5 swings within the allowable range, causing neither stopper bolt 15 to abut on pad 17, the vehicle body 11 is supported at three points defining a reverse triangle, i.e. at the left and right front wheels and the swing shaft 9, so that the fork lift truck usually travels like a tricycle that has a center of gravity within a triangle defined by a single front wheel and a pair of rear wheels.
In general, the fork lift truck is kept from tumbling when its body leans within a limit of floor inclination, and has "a stability against the tumbling in correspondence to an inner region of a triangular plane defined by support points of the body" (hereafter "vehicle body stability" or "stability"). The wider the region is, the greater the stability becomes.
The fork lift truck in concern however has a mast, which may have a significant lift height and may serve for carrying a heavy load lifted at a maximum height, with a significant rearward tilt, shifting a center of gravity of the vehicle body 11 toward the swingable rear axle 5. As the center of gravity moves rearward, the reverse triangle has a decreased transverse allowance for the stability, resulting in a reduced capacity.
The fork lift truck may travel at an accelerated speed on a flat road, with a "stableness". The stableness of travel is subjected to the three-point support system, and may be kept under a potential level. However, all the road is not flat.